The epididymis is critical to the process of sperm maturation because it provides a unique luminal fluid microenvironment that allows for sperm maturation and survival, and disruptions to this function lead to male infertility. However, disruptions to epididymal function may also arise as a consequence of abnormal fetal development, although very little is known either of the process of epididymal development or of the nature and causes of congenital defects that lead to male infertility. A major event during Wolffian/ epididymal duct embryonic development is elongation and coiling, presumably as a result of cell proliferation. However, in this application we hypothesize that an additional mechanism, cell intercalation contributes to elongation and coiling. Elongation and coiling is not a trivial event but must be highly coordinated with its specialized function of providing a unique luminal fluid microenvironment that is so important for sperm maturation. We have chosen the embryonic time period because cell proliferation and ductal coiling are initiated and it is a time when potential defects can occur. Examining the mechanism(s) of cell intercalation as a means to elongate and coil the Wolffian duct is novel, and we are especially interested in examining the contribution of a member of the planar cell polarity pathway (PCP), Ptk7, as a regulator of this important event during Wolffian duct morphogenesis. A combination of genetically modified mice, modern imaging techniques, in vitro organ culture techniques, and gene modifying approaches will be used to test the hypotheses outlined in the following three specific aims: (1) To test the hypothesis that Ptk7 plays an important role in cell shape and cell positioning, which in turn allow the Wolffian duct to undergo the morphogenic events of elongation and coiling. (2) To test the hypothesis that Ptk7 regulates specific cell rearrangements by modulating the basolateral protrusive activity and the orientation of cell division yet maintaining cell proliferaion during Wolffian duct embryonic development. (3) To test the hypothesis that cell intercalation during Wolffian duct elongation and coiling is driven by polarized changes in cytoskeleton organization, and is regulated by Ptk7 through activation of the Wnt/PCP pathway. In summary, the hypothesis that the Wolffian duct can elongate via cell intercalation is highly novel and innovative because it has always been assumed that elongation of the epididymal duct is via cell proliferation only. In addition, we have uncovered an unusual regulatory molecule, Ptk7, which is hypothesized to play a role in Wolffian duct elongation and coiling. The anticipated outcomes of this study will not only have a major impact on an area of reproductive biology that has been poorly understood, but will also contribute to our understanding of the fundamental process of tube morphogenesis. Specifically they will provide an understanding as to how the regulation of growth of the epididymis during development is important clinically.